Dowdell, Benjamin L.; Marfurt, Kurt
With the advent of horizontal drilling and hydraulic fracturing in the midcontinent USA, fields once thought to be exhausted are now experiencing renewed exploitation. However, traditional midcontinent seismic analysis techniques no longer provide satisfactory reservoir characterization for these plays, and new seismic analysis methods are needed to properly characterize these radically innovative play concepts. Our objective is to map tripolitic high porosity chert sweet spots within a highly fractured Mississippian lime reservoir, located in Osage County, Oklahoma, which also contains tight nonporous chert, using prestack impedance inversion correlated with surface seismic attributes and well log information from within the bounds of the 3-D seismic survey.
We begin by reprocessing a raw 3-D prestack seismic survey from Osage County, Oklahoma, USA, with the goal of performing a prestack time migration. We use surface-consistent deconvolution, paying careful attention to velocity analysis and coherent noise filtering. Once we are satisfied with the results of time processing, we migrate the prestack 3-D seismic data using an azimuthally binned Kirchhoff prestack time migration algorithm with an anti-aliasing operator, and then we apply a non-stretch NMO operator. Prestack time migration allows for better imaging of structure. The reflectors in our study area are mostly flat, so we expect to enhance subtle structure changes in comparison to a postack time migrated version of the survey. Seismic attributes such as prestack impedance inversion are sensitive to lithology while coherence and curvature are sensitive to lateral changes in waveform and structure. We use these attributes in conjunction with interpreted horizontal image logs to identify zones of high porosity and high fracture density.
Finally, having calibrated our results to well logs, we improve our understanding of the seismic behavoir of highly porous tripolitic chert which aids our characterization of this complex Mississippian carbonate reservoir.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013